Changing the Jenvey Throttle Lever

[AdamQ]

I'm a bit unhappy with my current throttle arrangement and a bit of research suggests that a quadrant as opposed to a lever should help matters.

 

A visit to the scrapyard yielded this (from a Corsa I think it was) which looks like it should do the trick.

 

Option 1 is to retain the existing lever, thus keeping the lugs for linking the two pairs of TBs and for the throttle stop, though I would have to remove part of the existing lever because of the geometry of the Corsa quadrant (ideally I need a mirror image of it).

 

Option 2 is to remove the existing lever and graft throttle stop and TB linking lugs onto the Corsa quadrant.

 

To get to the point, having looked at the TBs, it isn't obvious to me how the existing lever is held in place - can anybody enlighten me and maybe give a hint or to regarding removal?

 

Many thanks,

Adam

[keybaud]

I thought the Jenvey TBs used a quadrant to raise the lever. Are you trying to attach to the lever on the TBs without using the throttle linkage kit or do you just want a more linear progression?

 

Edited by - keybaud on 28 Mar 2013 12:04:15

[AdamQ]

At the moment, I just have this attached directly to the cable.

 

The Jenvey throttle linkage kit gets mixed reviews and is quite a price IMHO so I thought I'd investigate alternatives for obtaining a more linear progression - yes, that is what I'm after ...

[Drumster]

Adam,

 

I agree with you that the Jenvey linkage is not cheap, however my engineering/fabrication skills aren't too great so I opted to buy this when I converted to TBs. I have the over the top linkage and found it to be absolutely fine, no issues and throttle response is spot on.

 

Just my 2p worth

[keybaud]

Quoting AdamQ: 

At the moment, I just have this attached directly to the cable.

 

The Jenvey throttle linkage kit gets mixed reviews and is quite a price IMHO so I thought I'd investigate alternatives for obtaining a more linear progression - yes, that is what I'm after ...

 

The linkage kits often appear on Ebay and go for a lot less than the new price.

[AdamQ]

Thanks to you both for your input - appreciated.

 

To be fair, I think some of the slightly negative posts I came across were from quite a few years ago and I suspect the odd niggles - if indeed there were any - were ironed out a long time ago ...

 

Eyes peeled on ebay it is then ...

 

Would still be interested in how the lever is secured - went for another look earlier and it really does look like it's magic that holds it there ...

[Paul Deslandes]

You might find the second part of this article of interest. Even if you don't want or need to do the pedal box cable exit mod, the snail cam makes a huge difference to the lineareity and controllability of the throttle.

 

I don't think you can remove the lever which is why I used it to mount the cam.

Blat mail me if you want any further info.

 

Paul

[Drumster]

Adam,

 

Photo of linkage on TBs, the only thing different is that the adjuster on the pedal box has been angled down to ensure a straight run on the cable.

[oilyhands]

The quadrant is secured by a very small grubs crew which is perpendicular to the throttle spindle , it goes through the quadrant/lever and clamps to the shaft.

 

Oily

[AdamQ]

Thanks to all for the further replies.

 

Oily - mystery solved - thanks!

 

The pic confirms that the Jenvey linkage does indeed look the business.

 

Paul, thanks for the link - I came across your write-up in another recent post and it was largely that that set me on this path - just a lack of faith in my fabrication skills sent me to the scrapyard rather than the aluminium sheet shop!

 

All this has got me thinking about the ideal - I guess it's very subjective and varies with application/use, but presumably the rough aim is to have a constant percentage increase in RPM per unit of pedal travel as opposed to a constant absolute increase in RPM per unit - is that the gist of it or is there a lot more to it than that? Just thinking out loud really - always dangerous!

[combine]

Throttle linkage kit £36 including fittings, just had new one fitted as have had jenveys fitted a few weeks ago. Not used to the new set up as she's only recently been rr'd.

[ECR]

The quadrant mechanism gives a varying opening of the butterflies. The first (say) 10mm of cable movement opens the butterflies more than the last 10mm.

[Paul Deslandes]

I designed my quadrant snail cam to have a large radius at small throttle openings, decreasing as the amount of throttle increased. This makes the car very drivable in traffic and at low speed as its eliminates the kangaroo effect caused by too harsh a throttle, particularly on heavy breathing engines with big chokes. Once its over about 20 - 25% open, all hell breaks loose as the throttle opens more rapidly 😬

 

Paul

[combine]

Found it easy to stall on setting off from lights etc , not used to different linkage coming from carbs ! Bloody nusience !

[keybaud]

Quoting AdamQ: 

All this has got me thinking about the ideal - I guess it's very subjective and varies with application/use, but presumably the rough aim is to have a constant percentage increase in RPM per unit of pedal travel as opposed to a constant absolute increase in RPM per unit - is that the gist of it or is there a lot more to it than that? Just thinking out loud really - always dangerous!

 

It's not that simple, as linear rate of opening the throttle does not give a linear increase in air flow or engine revs. At low revs a 10% increase in throttle movement will open up the throttle body area to air flow by more than 10%, whilst the last 10% will be less than 10% (unless you happen have a square throttle body and butterfly); hence Paul's mod to his snail cam to reduce the rate of opening at low revs and increase it at high revs. You may want to change between 10% and 15% of power in traffic, but I doubt you ever want to control it between 85% and 90%. At the top end you're usually foot to the floor.

 

Edited by - keybaud on 29 Mar 2013 12:01:42

[AdamQ]

Whilst waiting for a Jenvey linkage to crop up on ebay, I've gone down this route. It seems to work OK, though I did need to add a return spring. I also needed to adapt my existing bracket - that was a T suspended from the underside of the TBs using two of the air filter back-plate bolts - the cross bar of the T interfered with the larger throttle cam - the T is now a Y and all seems to be well.

 

Keybaud, thanks for the explanation - your statement that

You may want to change between 10% and 15% of power in traffic, but I doubt you ever want to control it between 85% and 90%

makes perfect sense and illustrates the point very clearly.

 

Regarding

At low revs a 10% increase in throttle movement will open up the throttle body area to air flow by more than 10%, whilst the last 10% will be less than 10%

, is this indeed the case? According to my rather shaky maths, for a circular TB, the relationship between the open area of the TB and the angular rotation of the spindle looks like this (admittedly, for this to extend to the relationship between pedal movement and open area, a throttle cam/quadrant of constant radius is required) (and it also ignores the effect of the presence of the spindle on the open area, but that obviously only becomes a factor at high openings). The link suggests (shaky maths caveat again!) that 26° rotation (29%) is required to open up the first 10% of the TB area ...

 

Couldn't help exploring this as it's all quite interesting to me (must get out more!) ...

 

Thanks again to all for your input.

 

Adam

[keybaud]

Quoting AdamQ: 

At low revs a 10% increase in throttle movement will open up the throttle body area to air flow by more than 10%, whilst the last 10% will be less than 10%

, is this indeed the case? According to my rather shaky maths, for a circular TB, the relationship between the open area of the TB and the angular rotation of the spindle looks like this (admittedly, for this to extend to the relationship between pedal movement and open area, a throttle cam/quadrant of constant radius is required) (and it also ignores the effect of the presence of the spindle on the open area, but that obviously only becomes a factor at high openings). The link suggests (shaky maths caveat again!) that 26° rotation (29%) is required to open up the first 10% of the TB area ...

 

My flawed logic was based on a pencil and a drawing I made:

 

I drew a circle with a line across the middle. I found the spot 3/4 way down the vertical and draw a curve from the left hand and right hand edge of the middle line through the 3/4 line. The area below the curve appeared greater than the area between the curve and the middle line, implying that at 50% throttle, you have over 50% airflow. I now realise that I didn't take into account the fact that the rate of change of this curve isn't linear! I also didn't calculate the area, so I could be wrong twice.

[Jochen]

Has anybody the actual links for me as the old ones doesn’t work any longer ?

Many thanks in advance

[Paul Deslandes]

This one gives you my article on the roller and cam mods..

http://www.fastgrandad.co.uk/documents/Throttle%20cam%20and%20roller%20boss.pdf

Paul

[p.mole1]

I'm using the Jenvey Linkage, I had no option as I am now using a VVC head and my original cable linkage no longer fits.

In my case I had to use the underslung version which is a bit of a faf to set up and you have to file a bit off one throttle body. The throttle response is much nicer and the action on part throttle is more controllable.